Porous nanocomposite polymer hydrogels for water treatment

ABSTRACT

Synthesis, fabrication, and application of nanocomposite polymers in different form (as membrane/filter coatings, as beads, or as porous sponges) for the removal of microorganisms, heavy metals, organic, and inorganic chemicals from different contaminated water sources.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/009,060, entitled “Nanocomposite Hydrogel Polymer Beads forWater Treatment,” filed Jun. 6, 2014, the entire content of which ishereby incorporated by reference.

BACKGROUND

This disclosure pertains to the production and application of porousnanocomposite polymers for the removal of chemical and biologicalcontaminants from water.

Water is essential for life and is globally available in abundance, yet1 out of every 6 people living today does not have adequate access toclean water. Even though there are several drinking water treatmenttechnologies available today, they are not widely distributed andsuitable for all types of water contamination because they havedifferent treatment efficiencies and costs, and in some cases thesetechnologies require trained personnel.

Water contamination is exacerbated by vital industries such as leadsmelting, electroplating, petroleum and electronics, which dischargecontaminants into the environment. To deal with this problem, varioustechnologies have been developed to remove contaminants from wastestreams, such as coagulation, ion-exchange, chemical precipitation,membrane processes, and adsorption. However, most of these methodssuffer significant drawbacks, like high capital and operational costs,inappropriate efficiencies at usual discharge levels, and the productionof residual toxic sludge and secondary wastes that are difficult andexpensive to treat.

Set against the limitations above, adsorption has become a valuablealternative because of the low cost of adsorbent materials, lowoperating cost, high efficiency for dilute solutions, ease in handling,and minimal sludge production. More particularly, biosorption has beengetting considerable attention because biological materials arenaturally available, cheap and harmless. However, the biologicalmaterials utilized must be processed in unique ways in order to maintainor maximize adsorption capacity while also promoting strength anddurability.

SUMMARY

The present disclosure relates generally to the fabrication andapplication of porous nanocomposite polymers for the removal ofmicroorganisms, heavy metals, organic and inorganic chemicals fromdifferent water sources.

The porous nanocomposite polymers contain nanomaterials (carbon or metaloxide nanoparticles) that have anti-microbial properties and adsorptioncapacities for heavy metals and other cations. Additionally, uniquelydesigned metal oxide particles present in these beads havephotocatalytic capacity to enhance photochemical degradation of organicand biological contaminants in the water. Besides nanoparticles, theseporous nanocomposites are made of natural biopolymers that are easilyavailable, have low cost of fabrication and are biocompatible. Theunique blend of polymers in these nanocomposites makes possible for theremoval of both organic and inorganic chemicals, such as urea, humicacids, phosphates, nitrates, heavy metals and radioactive materials. Theprocess of fabrication is also facile and cost effective. The presentdisclosure relates to the synthesis of nanocomposite polymers for thesynthesis of porous hydrogel beads, porous nanobeads/colloids, surfaceor membrane coatings, and nanocomposite sponges for the removal ofchemical and biological contaminants in water. These nanocomposites canbe used in fluidized bed reactors or packed in columns with differentsizes or as coatings for membrane filtration, which will allow thetreatment of different volumes of water. Therefore, this system,depending on the size of the column, will serve to treat water fromsmall to large scales. The uniqueness of this system is that thenanocomposite polymers produced are multifunctional and can be easilyexpanded and modified to remove different pollutants in water.

In one example, graphene oxide (GO) was successfully incorporated into achitosan-poly (acrylic acid) (CS-PAA) polymer matrix. The nanocompositehydrogel beads have the ability to remove high levels of heavy metalfrom solution. These beads can be used in packed bed columns indifferent heights and flow rates to maximize the contaminant removal indiverse volumes of water.

Another example, graphene oxide (GO) was successfully incorporated intochitosan-Polyethylenimine (CS-PEI) polymer matrix or inalginate-Polyethylenimine (AG-PEI). These nanocomposites weresynthesized as porous hydrogel beads, colloidal (nanobeads) suspensions,and solid hydrogels or as a coating material for membranes and filters.These nanocomposites can also be freeze-dried to form porous sponges.These nanocomposites have the ability to remove high levels of heavymetals, total organic carbon (TOC), nitrates and phosphates. Thesenanocomposites can also be used in packed bed columns or in fluidizedbeds to maximize the contaminant removal in different volumes of water.

Chitosan (CS) is an example of a biosorbent used in removing heavymetals since it contains amine and hydroxyl groups that can formcomplexes with various heavy metal ions. CS is also an ideal materialsince it is derived from a naturally-occurring and abundant biopolymer,chitin, which is freely available in large quantities from seafoodprocessing waste. In order to use CS as an adsorbent, CS needs to becross-linked to improve its acidic resistance and enhance mechanicalstrength. The crosslinking process, however, decreases the number ofamine groups, which in return, reduces its adsorption capacity. Toovercome this issue, various polymers have been combined with chitosanvia surface modification or interpenetrating network in order to impartadditional functional groups and enhance CS sorption capacity. Inparticular, poly(acrylic acid) (PAA) has been incorporated into chitosanbecause it contains many carboxyl groups and has an anionicpolyelectrolyte form, which allows higher heavy metal removal.

Chitosan is a preferred polymer to make the beads because it occursnaturally in abundance, is biocompatible, has some anti-microbialproperties and is renewable since it is a waste product from the craband shrimp canning industries. Poly(acrylic) acid (PAA), is used in thisdisclosure as a preferred co-polymer because, like chitosan, it also hasheavy metal binding capacities, is commercially produced in large scale,and is widely used in various industries, agriculture, and medicine. PAAhas not been described as having any anti-microbial properties; however,several reports describe chitosan's and GO anti-microbial properties.

Other natural polymers besides chitosan, such as alginate, can also beused for the fabrication of polymer beads with nanomaterials. The PAA inthe beads can also be replaced by other functional polymers, such asPolyethylenimine (PEI), Poly(vinyl alcohol) (PVA), Poly (allyl aminehydrochloride), Cyclodextrin polyurethanes (CDP), and Triallylaminepolymer (TAP) among others to generate beads with capacity to removedifferent hazardous chemicals, such as anions, cations, and organicmatter.

Recently, nanomaterials have been increasingly used to remove heavymetals owing to their enhanced reactivity and higher specific surfacearea. When combined with polymers, they form a new line of nanohybridadsorbent materials. Graphene-based polymer nanocomposites are one ofthe most promising materials in this category. To date, no suchnanocomposite material incorporating GO into a CS-PAA or CS-PEI polymerhydrogel matrices has been synthesized and investigated for the removalof heavy metals, nitrate, phosphorous and TOC.

The addition of carbon based nanomaterials in the current nanocompositepolymer beads, such as graphene oxide, can enhance the adsorptioncapacity of these beads for heavy metals and inactivate microorganisms.Instead of adding graphene to these beads, it is also possible to addmetal oxide nanoparticles, such as, molybdenum oxide, zinc oxide andtitanium dioxide or nanohybrid nanoparticles, such as GO-MoO₂ andGO-TiO₂. These metal nanoparticles can enhance photo inactivation ofmicroorganisms and photocatalysis of organic chemicals in the water.

A significant advantage of the nanocomposite polymer is that thecombination of two or more polymers with nanomaterials can generateenhanced removal of organic and inorganic chemicals, as well asinactivation of microorganisms simultaneously. These nanocompositepolymers are also reusable and can be regenerated. They can be also usedto coat filters and membranes to enhance their water treatmentcapabilities.

A packed bed filtration device made up of the nanocomposite polymerbeads could be used for the treatment of fracking water, waste water,and water used by campers and travelers at rivers and lakes, and wouldbe particularly useful for the manufacture of different types of waterfilters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general scheme for the synthesis of porous nanocompositepolymers and the results of the dispersion. By combining alginate orchitosan with a functional co-polymer and the nanomaterials it ispossible with the addition of gluteraldehyde, to produce porousnanocomposite polymers.

FIG. 2 shows the different forms that the porous nanocomposites can beproduced. In the first picture, the first tube contains thenanocomposite in a solid hydrogel form, the second tube containsnanobeads of nanocomposite hydrogel particles in suspension, and thethird tube contains the freeze-dried nanocomposite hydrogel, whichformed a porous sponge. The second picture zooms in the freeze-driednancomposite hydrogel showing that it forms a porous sponge.

FIG. 3 shows the general scheme for coating surfaces, membranes andfilters with the nanocomposite polymers.

FIG. 4 shows the use of the porous nanocomposites beads for the removalof contaminants in water in a packed bed column;

FIG. 5 shows beads prepared containing 0%, 1%, and 5% graphene oxide(GO) in the chitosan-poly(acrylic) acid (CS-PAA) polymer blend, both asprepared and after cross-linking with glutaraldehyde;

FIG. 6 shows macroimages of different sizes of hydrogel beads produced;

FIG. 7 shows ATR-IR spectra of (a) CS-PAA with 5% GO, (b) CS-PAA and

-   -   (c) CS;

FIG. 8 shows ATR-IR spectra of (a) CS-PEI-GO, (b) CS, and (C) GO;

FIG. 9 shows scanning electron microscopy of a cross section of the beaddemonstrating the bead porosity;

FIG. 10 shows average removal of anionic contaminants in water byCS-PEI-GO. The initial concentration of the contaminants was: 50 ppm forTotal Organic Carbon (TOC) from humic acids, 4 ppm of InorganicPhosphate (KH₂PO₄), 10 ppm of Selenium (Se(IV)), and 11 ppm of NO³⁻N.

FIG. 11 shows average removal of 11 ppm of NO³⁻N in water byAlginate-PEI-GO and CS-PEI-GO, which demonstrate that alginate andchitosan are interchangeable in the nanocomposite since they givesimilar results;

FIG. 12 shows average removal of cationic contaminants at 10 ppm, suchas heavy metals by CS-PEI-GO;

FIG. 13 shows average removal of binary contaminants at 10 ppm byCS-PEI-GO;

FIG. 14 shows average removal of Pb²⁺ ions from solutions of various pHvalues by CS-PAA-GO nanocomposites;

FIG. 15 shows metal uptake rates and removal efficiencies of the CS-PAAbeads at different loading ratios;

FIG. 16 shows intraparticle diffusion kinetics for the adsorption oflead onto CS-PAA, GO1 and GO5 hydrogel beads;

FIG. 17 shows kinetic adsorption results showing the effect of contacttime on the adsorption of Pb²⁺;

FIG. 18 shows sorption data for three cycles utilizing dilute HCl asdesorption medium and using GO5 hydrogel beads;

FIG. 19 shows a comparison of the present nanocomposite beads withcurrent adsorbent materials on the market for the removal of lead;

FIG. 20 shows the synthesis of two types of molybdenum oxide (h- andα-);

FIG. 21 shows the degradation capacity of methyl blue dye by the twotypes of MoO₃ nanoparticles under fluorescent light (photocatalyticactivity of the nanomaterial);

FIG. 22 shows the inactivation capability of different types ofnanoparticles against E. coli;

FIG. 23 shows the scanning electron microscopy of cells exposed and notexposed to the nanoparticles of MoS₂ after light exposure. Showingphotocatalytic inactivation of microorganisms.

FIG. 24 shows microbial growth inhibition in the presence ofnanocomposite coated membranes.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present disclosure relates to the synthesis of nanocompositepolymers for the synthesis of porous hydrogel beads, porousnanobeads/colloids, surface or membrane coatings, and nanocompositesponges for the removal of chemical and biological contaminants inwater. The nanocomposite polymers are preferably used in a packed bedcolumns or fluidized bed reactors or as coatings in filter membranes(FIG. 4).

FIG. 1 shows a general scheme for the fabrication and application ofnanocomposite polymers in a packed bed column (FIG. 4). Polymers, suchas chitosan or alginate and poly(acrylic) acid (PAA) or polyethylenimine(PEI), are combined with nanomaterial fillers, such as graphene oxide(GO) or Molybdenum trioxide (MoO₃). This blend is then mixed withgluteraldehyde to cross-link the nanomaterials and polymers and producedifferent forms of nanocomposites. The nanocomposites haveanti-microbial properties that are effective against microbes due to theproduction of reactive oxygen species, facilitation of cellular damage,interruption of metabolic activity, and similar mechanisms. The beadsalso facilitate the adsorption and removal of contaminants, which isimpacted by functional groups, bead size, and pH. Packed bed columns orfluidized bed reactors containing the nanocomposite polymer beads orsponges can be used for effective removal of heavy metals and microbesfrom an influent contaminated water stream by passing it through thecolumn, with the residual metal concentration and microorganisms foundin the effluent stream being reduced. Flow rate and amount of beads inthe column may be adjusted to produce the desired results. Thesenanocomposites can also be used to coat membranes and filters for watertreatment.

One of the major challenges for incorporation of nanomaterials intonanocomposites is obtaining uniform dispersion in the polymer matrix.The combination of the polymers, such as CS and PAA or alginate and PEI,with the sonication method has been shown to uniformly dispersecarbon-based nanofillers in the CS-PAA matrix. The scheme of thepreparation of the nanocomposites and the results of the dispersion arepresented in FIG. 1. FIG. 1 shows well-dispersed suspensions of 1% and5% GO in CS-PAA composite. The GO remained well-dispersed three weeksafter preparation.

After the preparation of well-dispersed solutions of polymer compositeswith GO or MoO₃, beads are preferably synthesized by coagulation or byjust adding a crosslinking reagent (such as, but not limited to,gluteraldehyde, epichlorohydrin, glyoxal, and1-ethyl-3-(3-dimethylaminopropyl) carbodiimide together withN-hydroxysuccinimide) that will lead to the solidification of thenanocomposite polymers. For the chitosan, sodium hydroxide may be usedas a coagulant agent. In the case of alginate, hydrochloric acid may beused as a coagulant. Alternatively, the nanocomposite can be mixed withgluteraldehyde or other crosslinking reagents to form the beads or themembrane coatings without the need of a coagulant. FIG. 5 shows beadsprepared containing 0%, 1%, and 5% GO in the CS-PAA polymer blend. FIG.5 shows the beads as prepared and after cross-linking withglutaraldehyde. The size of the beads prepared was around 2 to 3 mm, butsmaller beads could also be achieved with a smaller syringe gauge toincrease the surface area-to-volume ratio (FIG. 6). The preparation ofalginate beads is also possible, replacing chitosan. Other polymersbesides PAA and PEI could also be incorporated into the chitosan oralginate polymer beads.

EXAMPLE 1 Synthesis of Nanocomposites Coatings for Membranes and Filters

The synthesis of alginate-polyethylenimine (PEI) andchitosan-polyethylenimine (PEI) polymer nanocomposites containinggraphene oxide (GO) was successfully achieved. The nanocomposites wereprepared in different forms (FIG. 2). It was possible to prepare thenanocomposite as a hydrogel block, a hydrogel micro and nanobeads, as asponge or as a coating material for membrane filtration (FIGS. 2, 3 and6).

The hydrogel nanocomposites were made of 0.2 to 4% alginate or chitosanas supporting materials for the co-polymers and nanomaterials to formsolid structures, such as beads, hydrogels, and sponges. Theconcentrations of the nanomaterials, in this case GO, were in the rangeof 0 ppm to 5000 ppm. The co-polymers, in this case PEI, had aconcentration of 5 to 30% (w/v %). After preparing this mixture,gluteraldehyde (0.5 to 5% (v/v %)) was added to crosslink the componentsof the nanocomposite mixture. For the filter preparation, thenanocomposite mixture containing gluteraldehyde was used for the coating(FIG. 3). For the filter, coagulation with NaOH or HCl was notnecessary. To form the hydrogel blocks or beads, the coagulation of thenanocomposites was done with NaOH or HCl. For the preparation of thesponges the hydrogel blocks were freeze-dried between 6 h to 24 hdepending on the size of the hydrogel blocks.

In order to characterize the nanocomposite produced and filter coatingswith the nanocomposites, the functional groups were determined throughattenuated total reflectance-infrared spectroscopy (ATR-IR) (FIG. 8).The nanocomposite mixture, as well as the pure chitosan and GOnanomaterials were deposited onto membrane filters and analyzed using aNicolet iS10 Mid Infrared FTIR Spectrometer (Thermo Fisher Scientific)equipped with a ZnSe crystal. Processing of the data was done usingOmnic 8 software (Thermo Fisher Scientific).

In a typical FTIR spectrum of chitosan, representative peaks includes2872 cm⁻¹ of C—H stretching vibration due to the pyranose ring, 1603cm⁻¹ of N—H stretching vibration in CO—NH group, 1156 cm⁻¹ of C—O—Canti-symmetric stretching vibration and 1082 cm⁻¹ of C—O stretchingvibration due to the pyranose ring, which are in accordance with theliterature (Yang, et al., 2010). Comparing with CS, several changes werefound in the spectrum of CS-PEI-GO. New bands appeared at 1730, 1620 and1362 cm⁻¹ and were attributed to the formation of C═O, C═N, and N—Oasymmetric stretch vibrations due to the successful incorporation of GOand PEI into chitosan.

EXAMPLE 2 Synthesis of Nanocomposite Beads

The synthesis of chitosan-poly(acrylic acid) (CS-PAA) polymer hydrogelbeads containing graphene oxide (GO) was successfully achieved. Thehydrogel beads used in this study were prepared using a one-steppreparation method that improved on already-facile methods developed forthe production of chitosan-based hydrogel beads (Dai, J., et al., Simplemethod for preparation of chitosan/poly(acrylic acid) blending hydrogelbeads and adsorption of copper(II) from aqueous solutions. ChemicalEngineering Journal, 2010. 165(1): p. 240-249, incorporated herein byreference). Chitosan (CS), poly(acrylic acid) (PAA) with an averagemolecular weight of 450,000, and methanol were purchased from SigmaAldrich. Graphite (−10 mesh, 99.9% metal basis) and NaOH were obtainedfrom Alfa Aesar. Glutaraldehyde (GLA), Pb(NO₃)₂, H₂SO₄, KMnO₄ and HClwere purchased from Fisher Scientific. NaNO₃ and H₂O₂ were obtained fromMerck and Macron, respectively. All the chemical reagents used wereanalytical grade and were used without further purification. All aqueoussolutions were prepared using deionized (DI) water. GO was synthesizedusing the modified Hummers' method (Hummers Jr, W. S. and R. E. Offeman,Preparation of graphitic oxide. Journal of the American ChemicalSociety, 1958. 80(6): p. 1339-1339, incorporated herein by reference.See also, I. E. M. Carpio, C. M. Santos, X. Wei and D. F. Rodrigues,Toxicity of a polymer-graphene oxide composite against bacterialplanktonic cells, biofilms, and mammalion cells. Nanoscale, 2012, 4,4746-4756, incorporated herein by reference).

To produce the hydrogel beads, 2% (wt/v) CS and 1.5% (wt/v) PAA wereprepared by dissolving in 0.5% (v/v) HCl solution. The use ofpolymerized acrylic acid has enabled the sequential dissolution of thedifferent components into a single polymeric solution that was at-onceready for co-precipitation in alkaline solution. In the production ofGO-nanocomposite beads, GO stock solution was prepared by dissolvingpowdered GO in 0.5% HCl solution with subsequent sonication to guaranteedispersion. This stock solution was added to the blended CS-PA polymersto obtain final products that contained 1% and 5% GO by weight withrespect to polymer content. Henceforth, such beads will be referred toas GO1 and GO5, respectively. Each solution was stirred for 20 h toensure homogeneity and left to stand for 22 h before dropping into 1.5 MNaOH solution stirred at 100 rpm. To control the bead size, thesolutions were placed inside syringes fitted with 23G1 Precision Glideneedles (BD) and dropped at a rate of 1 mL/min using a variable speedpump injector. The contact of the solution with basic media led toimmediate hydrogel bead formation. The beads were removed and washedwith copious amounts of water to remove the excess NaOH and until the pHwas neutral. Prior to adsorption testing, the beads were cross-linkedfor 30 min in 0.5% glutaraldehyde (GLA) solution and rinsed with DIwater to remove the excess GLA.

The prepared CS-PAA, GO1 and GO5 solutions showed good stability and noobservable phase separation occurred even after several months. Thisstability was maintained until hydrogel formation and enhanced with thecrosslinking process using GLA. Macroimages of the hydrogel beads areshown in FIG. 5 and they show spherical beads with an average diameterof 3 mm. FIG. 5 shows macroimages of (A) CS-PAA, (B) GO1 and (C) GO5hydrogel beads. The left side images for each pair are the as-preparedbeads while the ones on the right have been crosslinked with GLA.Crosslinking turned the opalescent CS-PAA beads into laser lemon colorwhile the color change was barely visible for the GO-infused beads. Whenthe wet beads were dried in a vacuum desiccator it was found that theCS-PAA, GO1 and GO5 beads had hydration values of 97.95%, 97.85% and97.74%, respectively. These values are reflective of the increase inpolymer mass with the addition of the graphene oxide nanomaterial.

In order to further characterize the hydrogel beads, functional groupswere determined through attenuated total reflectance-infraredspectroscopy (ATR-IR). The different polymer mixtures were depositedonto membrane filters and analyzed using a Nicolet iS10 Mid InfraredFTIR Spectrometer (Thermo Fisher Scientific) equipped with a ZnSecrystal. Processing of the data was done using Omnic 8 software (ThermoFisher Scientific). A hydration test was also conducted to determine thewater content and polymer mass using Eq. 1:

${{Hydration}\mspace{14mu}(\%)} = {\frac{( {W_{h} - W_{d}} )}{W_{h}} \times 100}$where W_(h) and W_(d) are the weights of the hydrated and dry beads,respectively. Drying of the beads was carried out in a vacuum desiccatoruntil constant weight.

The FTIR spectra (FIG. 7) were obtained for (a) GO5, (b) CS-PAA and (c)CS and the peaks observed were consistent with those reported inliterature. The peaks indicate the interactions of the polymers and thenanomaterial. The presence of characteristic PAA peaks in (b) relativeto (a) indicate the production of interpenetrating CS-PAA polymernetwork. Downshifted peaks in (a) are characteristic of the presence ofCS within the network. In the CS spectra, the overlapping peaks around3355 cm⁻¹ show the stretching vibrations of —OH and —NH. The peak at1633 cm⁻¹ corresponds to the bending vibration of the primary aminogroup while the peak at 1378 cm⁻¹ show the C—H stretching vibration ofthe alkyl group of the polymeric structure. On the other hand, the peakat 1070 cm⁻¹ shows the —C═O stretching vibration. With the addition ofPAA, a sharp peak at 1709 cm⁻¹ is observed which shows the —COOHstretching vibration. Peaks at 1566 cm⁻¹ and 1409 cm⁻¹ are also observedto occur corresponding to the asymmetric and symmetric vibrations of—COO⁻, respectively. The presence of these peaks indicates thesuccessful blending of PAA and CS. Meanwhile, the similarity of the GO5curve to that of the CS-PAA curve indicates that the addition andco-precipitation of GO did not significantly alter the CS-PAAsemi-interpenetrating polymer network nor destroy the functional groupspresent. However, downshifting is noted for the 1566 cm⁻¹, 1640 cm⁻¹ and2933 cm⁻¹ peaks, the latter of which corresponds to the C—H stretchingvibration of the alkyl group. The downshifting indicated the presence ofthe interaction of GO with the polymeric network which is mainlyphysical in nature.

EXAMPLE 3 Batch Lead Adsorption Experiments

Stock solutions of 2,000 mg/L Pb²⁺ were prepared by dissolvingappropriate amounts of Pb(NO₃)₂ in Millipore water. Different workingsolutions for the batch adsorption experiments were obtained by serialdilution of the prepared stock. The batch adsorption experiments wereconducted at room temperature in covered Erlenmeyer flasks using aplatform shaker (New Brunswick Scientific) at 130 rpm. Pb²⁺ analyseswere done using an AAnalyst 200 Atomic Adsorption Spectrometer(PerkinElmer).

The effect of pH on the adsorption rate was evaluated at the pH range of2.0-6.0. The initial pH values of Pb²⁺ solutions were adjusted using 0.1M and 0.01 M HCl and NaOH solutions. Adsorption assays were carried outfor 24 h using 40 mL of 100 ppm Pb²⁺ solution. The metal uptake, Q(mg/g), was calculated according to Eq. 2:

$Q = \frac{( {C_{0} - C_{e}} )V}{m}$where C_(o) (mg/L) and C_(e) (mg/L) are the initial and final Pb²⁺concentrations in solution, respectively, V (L) is the volume of Pb²⁺solution, and m (g) is the weight of dry hydrogel beads.

It is generally observed that the uptake capacity of adsorbent materialsis affected by solution pH. For this reason, the removal of Pb²⁺ ions bythe CS-PAA, GO1 and GO5 hydrogel beads was investigated at pH valuesranging from 2.0 to 6.0 and the results are shown in FIG. 14. FIG. 14shows average removal of Pb²⁺ ions from solutions of various pH values.The effect of pH on adsorption is significant for all materials testedand removal is significantly better starting at pH 4.0. Note theconsistently better performance of the GO-infused beads over the CS-PAAhydrogel beads and the enhanced removal owing to the addition of morenanomaterial as shown by the better performance of GO5 over GO1.Experimental conditions: Pb²⁺ concentration 100 mg/L, volume 40 mL,dosage 25 g/L, pH range 2.00-6.00, time 24 h.

From FIG. 14, it can be seen that the adsorption capacities of the threehydrogel beads are greatly affected by pH values and the metal uptakeproperties of the hydrogel beads improved dramatically starting from pH4.0. This behavior can be attributed to the effect of pH on theionization states of the functional groups that are present in theadsorbent materials as well as on the solubility of lead in solution.For CS and PAA, the increased acidity caused the protonation of theamine and carboxyl groups thereby inducing an electrical repulsion withthe positively-charged lead ions and limiting adsorption. At higher pH,these functional groups get deprotonated and the end effect is theincrease of the metal uptake. Adding GO into the polymer matrix onlyserved to magnify this trend. GO added additional —COOH and —OHfunctional groups and at pH 5.0-7.0 it is theorized that thesefunctional groups became deprotonated and the resulting —COO⁻ and —O⁻species provided electrostatic attraction for the positively-chargedmetal ions. Thus even at very small fractions, the amount of GO in thepolymer matrix increased the adsorption capacity of the beadssignificantly.

While removal at pH 6 was highest, spontaneous precipitation of leadhydroxide was observed during pH adjustment to this level. To preventthe contribution of metal precipitation in the removal mechanism,subsequent tests were done at pH 5. The choice of this pH value does notin any way limit real-world applicability since most industrialwastewaters are moderately acidic with pH values between 5 and 6.

The effect of adsorbent dosage was conducted by adding different massesof CS-PAA hydrogel beads into 40 mL of 100 ppm Pb²⁺ solution andallowing contact for 24 h. The metal uptake rates were determined usingEq. 2 while the removal efficiencies were measured using Eq. 3:

${{Removal}\mspace{11mu}(\%)} = {( {1 - \frac{C_{e}}{C_{o}}} ) \times 100}$

In order to determine the minimum optimal performance among the threematerials, the efficiency of the CS-PAA beads was evaluated at differentloading ratios ranging from 25.0-68.75 g/L of beads in 40 mL of Pb²⁺solution at pH 5.0. FIG. 15 shows metal uptake rates and removalefficiencies of the CS-PAA beads at different loading ratios. While anincrease in adsorbent dose results in better Pb²⁺ removal there is acorresponding decrease in metal uptake rates indicating a decrease inefficiency mainly due to the increase in the number of unsaturated sitesthat remained unutilized at equilibrium. Experimental conditions: Pb²⁺concentration 100 mg/L, volume 40 mL, dosage 25.00-68.75 g/L, pH 5.0,time 24 h.

As can be seen in FIG. 15, the beads show lead removal rates rangingfrom 45.5% at the lowest dosage of 25.0 g/L up to 99.6% at the highestdosage of 68.75 g/L. The increase in lead removal is due to the increasein polymer material and the corresponding additional surface area thataccompanied this increase. The added surface area meant extra sites foradsorption and this contributed to a 118.9% overall increase in leadremoval. However, analysis of the lead uptake curve showed an oppositetrend, decreasing by 20.9% per unit mass of CS-PAA when the dosage wasincreased. This decrease in efficiency is due to the fact that once theinteraction between Pb²⁺ and the CS-PAA beads had reached equilibrium,the presence of more adsorbent material translated to some sitesremaining unsaturated and therefore unutilized for adsorption. Factoringthis added mass into the calculation for lead uptake resulted to asmaller Q value. As the figure indicated, the most economical dosage forthe system was 37.5 g/L of CS-PAA beads corresponding to 1.5 g hydrogelbeads per 40 mL of Pb²⁺ solution and this ratio was used for thesucceeding tests.

Kinetic studies were carried out by adding hydrogel beads to 80 mL of100 ppm Pb²⁺ solution at pH 5.0. At predetermined times (5-1440 min),0.5 mL of aliquots were extracted and analyzed for residual Pb²⁺concentrations. Meanwhile, a same amount of water at pH 5.0 was addedinto the bulk solution in order to keep the total volume constant. Theadsorption rate at any time t, Q(t_(i)) (mg/g), was calculated using Eq.4:

${Q( t_{i} )} = \frac{{( {C_{o} - C_{t_{i}}} )V_{o}} - {\sum\limits_{2}^{i - 1}{C_{t_{i}}V_{s}}}}{m}$

where C_(o) and C_(ti) (mg/L) are the initial Pb²⁺ concentration andPb²⁺ concentration at t_(i), respectively; V_(o) (L) is the volume ofPb²⁺ solution and V, (L) is the aliquot volume extracted for analyticalpurposes. Polymer mass, m (g), is reported dry.

Adsorption kinetics is an indispensable tool in adsorption studiesbecause it provides understanding of the removal rates of pollutantsfrom aqueous solutions. At the same time it also allows examination ofthe adsorption behavior and whether such can be described by predictivetheoretical models. FIG. 16 shows kinetic adsorption results showing theeffect of contact time on the adsorption of Pb²⁺, or the removal of leadions by the three different hydrogels with respect to time. Lead removalwas very fast during the first 60 min of treatment indicating rapidinitial external surface deposition mechanism followed by slowerinternal diffusion. CS-PAA removed 86.48 mg/g Pb²⁺ and the addition ofnanomaterial increased the metal uptake by 20.51% for GO1 and 27.39% forG05. Experimental conditions: Pb²⁺ concentration 100 mg/L, volume 40 mL,dosage 37.5 g/L, pH 5.0, time 5-1440 min. FIG. 16 also clearly showsthat removal was enhanced with the addition of nanomaterials and thatthe amount of GO posted a positive effect on lead removal. It can alsobe seen that increase in adsorption was minimal during the last 12 h oftreatment. This phenomenon indicated that overall the adsorptionmechanism started with a rapid external surface deposition followed by amuch slower internal diffusion process which may be rate-determining.

In order to examine the adsorption mechanisms, it was necessary todetermine the kinetic parameters of the adsorption process using severalmodels. In this work, the pseudo first-order, pseudo second-order andthe intraparticle kinetic diffusion models were applied to theexperimental data. The pseudo first-order model is linearized using Eq.6:ln(Q _(e) −Q _(t))=ln Q _(e) −k ₁ t

The pseudo second-order models is linearized using Eq. 7:

$\frac{t}{Q_{t}} = {\frac{1}{k_{2}Q_{e}^{2}} + \frac{t}{Q_{e}}}$

For both equations, Q_(e) snd Q_(t) are the amounts of Pb²⁺ adsorbedonto the hydrogel beads (mg g⁻¹) at equilibrium and at any time t (min),respectively. The respective rate constants for the pseudo first-orderand pseudo second-order adsorption are given by k₁ and k₂ (min⁻¹).Meanwhile, the intraparticle diffusion model used Eq. 8:Q _(t) =k _(p) t ^(0.5)where k_(p) (mg g⁻¹ min^(−1/2)) is the intraparticle diffusion rateconstant.

The experimental data were plotted using the linearized forms of thepseudo first- and second-order kinetic models and the regressionformulas were used to obtain the kinetic parameters for the adsorptionof lead, which are presented in Table 1 below. Investigation of the datafor pseudo first-order kinetics shows a big discrepancy between theexperimental and calculated Q_(e) values for the three adsorbentmaterials. For the pseudo second-order kinetic model these values are inclose agreement and this consistency is confirmed by the extremely highcorrelation coefficients of more than 0.99 which are higher than thoseobtained for the pseudo-first order kinetics. These results indicatedthat the adsorption of lead onto the three hydrogel materials is bestdescribed by the pseudo second-order kinetic model and that therate-determining step was chemisorption involving valence forces betweenthe lead ions and the adsorbent materials either through sharing orexchange of electrons.

TABLE 1 Experimental data and calculated parameters for the pseudofirst- and second- order kinetic models for the adsorption of Pb²⁺ ontoCS-PAA, GO1 and GO5 Pseudo first-order Pseudo second-order Q_(exp) k₁ ×10⁻³ Q_(e,cal) k₂ × 10⁻³ Q_(e,cal) H Beads (mg g⁻¹) (min⁻¹) (mg g⁻¹) R²(g mg⁻¹ min⁻¹) (mg g⁻¹) (mg g⁻¹ min⁻¹) R² CS-PAA 86.48 5.50 63.82 0.9940.22 89.77 1.78 0.999 GO1 104.22 4.12 73.67 0.985 0.16 107.87 1.84 0.999GO5 110.17 3.75 77.60 0.981 0.14 113.90 1.83 0.998

A plot of Q versus t^(0.5) (FIG. 17) was constructed in order todetermine the fit of the experimental data to the intraparticlediffusion model. FIG. 17 shows the intraparticle diffusion kinetics forthe adsorption of lead onto CS-PAA, GO1 and GO5 hydrogel beads. Theresult is a non-linear plot across the time range which, upon closeexamination and linearization, reveals the presence of three regionsimplying a multi-stage adsorption process. The first stage (I) ischaracterized by the rapid external diffusion and adsorption at thesurface, the second stage (II) is characterized by slow intraparticlediffusion while the third (III) stage is characterized by even slowerintraparticle diffusion. The existence of the regions is confirmed bythree parametric values k_(p1), k_(p2) and k_(p3) (Table 2 below), whichcorrespond to the rate diffusion constants for regions I, II, and III,respectively. Since k_(p1) is the highest among the three values, itmeans that the transfer of the lead ions from the bulk phase to thesurface occurred the fastest. The lower k_(p2) value shows that thepenetration of the lead ions into the inner matrix for the materialsoccurred more slowly and was therefore rate-limiting, confirming earlierfindings. The lowest k_(p3) value resulted from the depletion of leadmetal ions from the solution and the establishment of equilibrium atthis stage.

TABLE 2 Parameters for the intraparticle diffusion model for theadsorption of Pb²⁺ onto CS-PAA, GO1 and GO5 showing the presence ofthree stages for adsorption. Material k_(p) R² CS-PAA k_(p1) (mg g⁻¹min^(−0.5)) 6.19 0.986 k_(p2) (mg g⁻¹ min^(−0.5)) 1.49 0.957 k_(p3) (mgg⁻¹ min^(−0.5)) 0.83 GO1 k_(p1) (mg g⁻¹ min^(−0.5)) 6.50 0.991 k_(p2)(mg g⁻¹ min^(−0.5)) 1.87 0.966 k_(p3) (mg g⁻¹ min^(−0.5)) 0.91 GO5k_(p1) (mg g⁻¹ min^(−0.5)) 6.32 0.995 k_(p2) (mg g⁻¹ min^(−0.5)) 2.000.965 k_(p3) (mg g⁻¹ min^(−0.5)) 0.93

Since the hydrogel beads that contained GO showed marked improvementsover the hydrogel beads composed purely of polymers, it can be said thatthe addition of the nanomaterial into the polymer matrix increased theintraparticle diffusion rate. At the same time, it is also observed thatthe amount of GO added had a positive effect on the removal rate thusexplaining why the GO5 beads performed better than the GO1 beads.

Adsorption equilibrium studies were conducted by adding differenthydrogel beads to 40 mL of 100-ppm Pb²⁺ solutions at pH 5.0 and allowingcontact for 24 h. The initial lead concentrations were varied from50-350 mg/L and the metal uptake rates (Eq. 2) were used in fitting intoLangmuir and Freundlich equations.

Adsorption equilibrium studies are important because they enableunderstanding of the interactive behaviors between solutes andadsorbents. This knowledge is necessary since it is essential in thedesign and optimization of adsorption systems and processes. Since a newmaterial was developed in this study, the equilibrium data were fittedusing the Langmuir and Freundlich isotherm models which are capable ofexpressing the relationship between the lead ions and the new hydrogelmaterials. The Langmuir isotherm model is based upon the assumption thatthe uptake of metal ions occurs on a structurally homogeneous adsorbentsurface by monolayer adsorption where all the adsorption sites areidentical and energetically equivalent and there is no interactionbetween the adsorbed ions. The linear form of the model is given as Eq.9:

$\frac{C_{e}}{Q_{e}} = {\frac{1}{{bQ}_{\max}} + \frac{C_{e}}{Q_{\max}}}$where Q_(max) (mg g⁻¹) is the maximum adsorption capacity of theadsorbent material, Q, (mg g-1) is the amount of lead ions adsorbed atequilibrium, C_(e) (mg L⁻¹) is the lead concentration in the liquidphase at equilibrium, and b (L mg⁻¹) is the Langmuir adsorptionconstant. In addition, a dimensionless constant R_(L), called theequilibrium parameter, is calculated in order to identify whether theadsorption process is favorable (1>R_(L)>0), linear (R_(L)=1),unfavorable (R_(L)>1), or irreversible (R_(L)=0). This value is computedusing Eq. 10:

$R_{L} = \frac{1}{1 + {b\; C_{0}}}$where C_(o) (mg g⁻¹) is the initial lead concentration.

On the other hand, the Freundlich isotherm is based on the assumptionthat the adsorption of pollutants occurs on a heterogeneous surfacethrough multilayer adsorption with the amount of solute adsorbedincreasing infinitely with an increase in concentration. The linear formof the model is given by Eq. 11:

${\log\; Q_{e}} = {{\log\; K_{f}} + {\frac{1}{n}\log\; C_{e}}}$where K_(f) and n are the Freundlich constants related to adsorptioncapacity of adsorbent and adsorption intensity, respectively. The valueof n represents the favorability of the adsorption, where a value of nless than one indicates favorable adsorption over the entire range ofconcentration studied while a value of n greater than one means that theadsorption is favorable at high concentrations.

The isotherm data were plotted using the linearized equations of theisotherm models and the regression formulas were used to derive theisotherm parameters which are shown in Table 3 below. Looking at thecorrelation coefficients (R²) of the Langmuir isotherms for the threehydrogel materials, it can be seen that these are very close to 1.0 andthat these values are consistently greater than the R² values for theFreundlich isotherm. As such, the Langmuir isotherm model is moreappropriate in describing the adsorption process and it can therefore besaid that the mechanism for adsorption is monolayer on the homogeneoussurfaces of the three different adsorbent materials.

TABLE 3 Parameters of the Langmuir and Freundlich isotherm models forthe adsorption of Pb²⁺ onto CS-PAA, GO1 and GO5. Langmuir isothermFreundlich isotherm Beads Q_(max) (mg/g) b (L mg⁻¹) R_(L) R² K_(f) n R²CS-PAA 109.89 0.16 0.0180 < R_(L) < 0.9993 73.08 14.01 0.9885 0.0745 GO1116.28 0.39 0.0075 < R_(L) < 0.9995 90.51 21.79 0.9734 0.0322 GO5 138.890.47 0.0062 < R_(L) < 0.9992 119.37 44.05 0.7708 0.0199

To determine the adsorption capacities of the materials, the LangmuirQ_(max) values were calculated and it can be seen that the capacity ofthe hydrogel beads to adsorb lead greatly improved with the addition ofGO. This enhancement occurred because GO increased the overall surfacearea for adsorption as it also provided additional functional groups.This allowed the beads to attain maximum adsorption capacities higherthan those of other sorbents reported in literature (Table 4 below). Itcan also be observed that the binding energy, b, of the sorption systemincreased with the addition of GO and that the binding energy increasedwith the increase in GO content. When the equilibrium parameter, R_(L),values were calculated for the three nanocomposite materials it wasfound that the adsorption of lead was favorable for all cases. This canbe gleaned from the R_(L) values which were all between zero and one.Comparison of the values also indicated that the addition of GO into theCS-PAA polymer matrix enhanced the affinity since a greater affinitybetween the adsorbate and adsorbent can be inferred when R_(L) issmaller. Furthermore, inspection of the n values show that leadadsorption was favorable at high concentrations for all threenanocomposite materials since all the n values were greater than unity.The addition of GO into the matrix also enhanced the favorability asshown by the fact that the CS-PAA hydrogel beads had a lower n valuethan the GO-infused beads. The relative GO content also had a positivebearing on the favorability as shown by the larger n value for GO5relative to the n value for GO1.

TABLE 4 Comparison of Pb²⁺ removal capacities of the hydrogel beadsproduced in this study and sorbents cited elsewhere based on maximumadsorption values of the Langmuir model. Q_(max) Material (mg g⁻¹) MWCNT58.26 Coated bentonite 95.88 Activated carbon 51.81 Chitosan beads 34.98Activated carbon 43.85 Magnetic nanoparticles 40.10 PVA-PEI nanofibers90.03 CS-PAA beads 109.89 GO1 beads 116.28 GO5 beads 138.89

EXAMPLE 4 Desorption and Reusability Experiments

Reusability experiments were conducted for the GO5-infused beads bysubjecting the hydrogel beads to three adsorption-desorption cycles. Foreach adsorption cycle, the beads were shaken in 100 ppm Pb²⁺ solutionsat pH 5.0 for 24 h at a ratio of 1.5 g beads per 40 mL metal solution.For desorption, the beads were shaken in 50 mL of 0.1 M HCl solution for24 h and the desorption efficiencies were calculated using Eq. 5:

${{Desorption}\mspace{14mu}(\%)} = {( \frac{C_{e,d}V_{d}}{( {C_{o,a} - C_{e,a}} )V_{a}} ) \times 100}$where C_(e,d) and V_(d) refer to the equilibrium concentration andvolume of desorption solution, respectively; C_(o,a) and C_(e,a) referto the initial and equilibrium concentrations of the adsorptionsolution, respectively; and V_(a) refers to the volume of adsorptionsolution. Prior to each desorption cycle, the beads were washed withdeionized water to remove adhering lead solution. Since the beads comeout acidic after each desorption cycle, it was necessary to equilibratethem with alkaline water to ensure that the succeeding adsorption takesplace at the desired pH.

Cost is a crucial consideration in the evaluation of new adsorbentmaterials since adsorbent cost has a significant bearing on the economicfeasibility of the treatment process. Focusing on the most efficientamong the three hydrogel materials, the reuse potential of GO5 was theninvestigated by subjecting it to several cycles ofadsorption-desorption. In this case, the desorption was carried out inbatches using low-concentration hydrochloric acid which has been showneffective in desorbing Pb²⁺ from polymeric materials. FIG. 18 shows thesorption data for three cycles utilizing dilute HCl as desorption mediumand using GO5 hydrogel beads as model adsorbent owing to its superiorperformance. The experimental data as depicted in FIG. 18 show thatdesorption is very effective throughout the three cycles tested.Complete desorption was attained on the first cycle, 99.0% on the secondcycle and 92.3% on the third cycle. As for the adsorption behavior, GO5exhibited excellent metal uptake ability. Lead adsorption using freshbeads was 99.6% in the first cycle, 95.9% in the second cycle and 89.7%in the third cycle. The relatively high values obtained for both leadadsorption and desorption show that the polymer beads can be regeneratedand reused for at least three cycles. This regenerative abilityindicates good reusability and shows that the nanocomposite polymerbeads could be applied to remove lead from water and wastewater withgood feasibility.

EXAMPLE 5 Comparative Lead Removal Capacity

Studies were conducted with the nanocomposite beads to determine theirlead removal capacity, as described above. The preliminary results withthe CS/PAA, CS/PAA containing 1% and 5% GO showed that the presence of5% GO in the polymer composite beads enhanced lead removal by 20%compared to the CS/PAA beads alone (FIG. 19). Also a literature reviewcomparing the new nanocomposite with previously known lead sorbentsshowed that the new nanocomposites have a significantly better leadremoval capacity (FIG. 19).

Results of the chitosan-PEI-GO (FIGS. 12 and 13) also show that thepresence of the co-polymer can lead to different adsorption capacitiesfor different heavy metals. For instance CS-PAA-GO performed better forPb(II) than CS-PEI-GO, while CS-PEI-GO performed better for Cr(VI) andCu(II). Due to the nature of the co-polymers, it is possible to makenanocomposites with affinity for different heavy metals.

Results from FIG. 13, also show that the presence of other heavy metalcontaminants in the solution might lead to a synergistic heavy metalremoval, since higher removal was observed with a positively and anegatively charge metal were simultaneously present in the water.

EXAMPLE 6 Comparative Antimicrobial Properties

Coated surfaces with nanomaterials, such as GO, MoO₃ and MoS₃ showedmicrobial inactivation higher than 85% (FIG. 23). GO presentedantimicrobial activity in the dark or under light. In the case of MoO₃and MoS₂, they performed better under visible light conditions. Theseresults show that MoO₃ and MoS₂ have photocatalytic activity that leadsto their antimicrobial properties.

These nanomaterials can also be incorporated into the polymers andpreserve the antimicrobial properties. In FIG. 24, it is possible tovisualize that the nanocomposites have antimicrobial properties and havehigher microbial growth inhibition than the pure chitosan or thenon-coated membranes.

EXAMPLE 7 Alternatives

The fabrication of chitosan beads with functional polymers, such as PAA,can be extended to other polymers, such as Polyethylenimine (PEI),Poly(vinyl alcohol) (PVA), Poly (allyl amine hydrochloride),Cyclodextrin polyurethanes (CDP), and Triallylamine polymer (TAP) amongothers to generate beads with the capacity to remove different hazardouschemicals, such as anions, cations and organic matter, other than heavymetals only. Table 5 below shows various useable polymers and theircontaminant removal properties.

TABLE 5 Polymer Contaminant Removal Triallylamine polymer Anions (e.g.CrO₄ ²⁻, PO₄ ³⁻, NO₃ ⁻, MnO₄ ⁻) (TAP) Polyethylenimine Anions (e.g. CrO₄²⁻, PO₄ ³⁻, NO₃ ⁻, organic (PEI) matter). Poly(acrylic acid) (PA)Cations (e.g. Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺) Cyclodextrin Organic matterpolyurethanes (CDP) Poly (allyl amine Anions (e.g. PO₄ ³⁻, NO₃ ⁻, NO₂ ⁻)hydrochloride) (PAA) Poly(vinyl alcohol) Cations (e.g. heavy metals)(PVA)

Molybdenum oxide can also be used in the beads, since it can beactivated by fluorescent or sun light to remove dyes from the waterthrough a photocatalytic reaction. FIG. 19 shows the synthesis of twotypes of Molybdenum oxide (h- and α-). FIG. 21 shows the degradationcapacity of Methyl Blue dye by the two MoO₃ nanoparticles underfluorescent light. The h-MoO₃ has better degradation capacity thanα-MoO₃.

These nanoparticles also show anti-microbial properties. FIG. 22 showscellular damage caused by the presence of MoS₂ nanoparticles. Thesenanoparticles were photoactivated by visible light. FIG. 23 shows thatthe anti-microbial properties of different nanoparticles, such as GO,h-MoO₃ and MoS₂ are similar. However, h-MoO₃ and MoS₂ shows higherantimicrobial activity, as seen in FIG. 22, when in the presence ofvisible light.

REFERENCES

The following references, to the extent that they provide exemplaryprocedural or other details supplementary to those set forth herein, arespecifically incorporated herein by reference.

Non-Patent Publications

-   -   Dai, J.; Yan, H.; Yang, H.; Cheng, R., Simple method for        preparation of chitosan/poly(acrylic acid) blending hydrogel        beads and adsorption of copper(II) from aqueous solutions.        Chemical Engineering Journal 2010, 165, (1), 240-249.    -   Yang, X.; Tu, Y.; Li, L.; Shang, S.; Tao, X., Well-Dispersed        Chitosan/Graphene Oxide Nanocomposites. ACS Appl. Mater.        Interfaces, 2010, 2 (6), pp 1707-1713.    -   Hummers Jr, W. S. and R. E. Offeman, Preparation of graphitic        oxide. Journal of the American Chemical Society, 1958. 80(6): p.        1339-1339.    -   I. E. M. Carpio, C. M. Santos, X. Wei and D. F. Rodrigues,        Toxicity of a polymer-graphene oxide composite against bacterial        planktonic cells, biofilms, and mammalion cells. Nanoscale,        2012, 4, 4746-4756.

What is claimed is:
 1. Nanocomposite polymer hydrogel for watertreatment comprising: polymer matrix material, wherein the polymermatrix material comprises one or more natural biopolymers and one ormore co-polymers, wherein at least one natural biopolymer is chitosan oralginate, and wherein at least one co-polymer is poly(acrylic) acid(PAA) or polyethylenimine (PEI); and nanoparticles uniformly dispersedthroughout the polymer matrix material in an amount of about 1% to about5% by weight of the polymer matrix material, wherein the nanoparticlesare graphene oxide (GO), wherein the nanocomposite polymer hydrogel iscross-linked, wherein the nanocomposite polymer is formed into poroushydrogel beads, porous hydrogel colloids, porous hydrogel sponges, orhydrogel coatings, and wherein the nanocomposite polymer hydrogel iscapable of adsorption and removal of lead and other contaminants fromwater.
 2. A packed bed column filtration device or fluidized bedcomprising the nanocomposite polymer hydrogel of claim
 1. 3. Thenanocomposite polymer hydrogel of claim 1, wherein the one or morenatural biopolymers is chitosan and the one or more co-polymers ispoly(acrylic) acid (PAA).
 4. The nanocomposite polymer hydrogel of claim1, wherein the graphene oxide (GO) is present at about 5% by weight withrespect to the polymer matrix material.
 5. The nanocomposite polymerhydrogel of claim 1, wherein the one or more co-polymers furthercomprises a co-polymer selected from the group consisting of poly(vinylalcohol) (PVA), poly(allylamine hydrochloride), cyclodextrinpolyurethanes (CDP), triallylamine polymer (TAP), and mixtures thereof.6. A method for the removal of contaminants from a contaminated waterstream, comprising: passing the contaminated water stream through thepacked bed column filtration device or fluidized bed of claim 2 toremove at least some of the contaminants from the water stream.